Antarctic krill presents one of the most attainable large-scale sources of significant expansion of the production of protein-containing food produce of animal origin. The catches of krill may well surpass the total catches of fish in the World Ocean at their present level. The most valuable component of krill is its pure meat in the form of lumps of the muscular tissue, the chemical composition of krill meat being close to that of the meat of crabs and shrimps and containing numerous vital aminoacids and microelements. For krill meat to be used as food, it has to be completely separated from the shell. Pure meat obtained from krill should have the minimum content of lipides and be devoid of the remnants of the liver and of the contents of the gastrointestinal tract, which impairs the quality of the final product and curtail its storage time.
When one considers that krill is caught in remote areas, which entails prolonged transportation to consumers, it becomes clear that it is expedient to process krill directly in the catching regions and to produce therefrom pure meat as either a ready-to-use product, e.g. natural canned meat, or else as a semi-finished product, e.g. deep-frozen meat.
There is known an apparatus for removing the shell of crustaceans, including a belt conveyor, a spiral or helical duct and a rotary disc with sharp spikes on its periphery.
The known apparatus operates, as follows.
Crustaceans are loaded with aid of the belt conveyor into the feed channel of the helical duct. The action of the rotating disc makes the crustaceans advance with acceleration along the predetermined path, the sharp spikes of the rotating disc incising the shell surface and destroying it. Then the meat and shell fragments are separated by flotation.
The known apparatus enables a processor to obtain the meat of shrimp in the form of individual lumps; however, these lumps are intensely crushed and disintegrated, and as a result there is a considerable loss of meat. This apparatus is predominantly intended for treating fairly large shrimp, but cannot be applied for use in removing the shell of small shrimp, e.g. of antarctic krill.
There are known devices for separating the heads of shrimps from their bodies, including a loading funnel, a guiding duct, a shrimp-processing chamber with a stationary cutting member and a pipe for feeding the working fluid.
In these known devices shrimps are fed in one-by-one fashion into the loading funnel and each shrimp advances along the guiding duct into the processing chamber where it is acted upon by a high-velocity liquid jet. The area of the connection of the head part of the shrimp is positioned adjacent to the edge of the stationary cutting member, and the effort produced by the high-velocity liquid jet is directed either at the head part or at the body of the shrimp, whereby the head and the body become separated.
These known devices perform but some of the operations of the technology of processing crustaceans, namely, those involved in separating the head from the body. The subsequent operations of destroying the shell and recovering the meat are performed by other devices, the succession of numerous operations all inadvertently involve some meat losses and generally impair the taste of the final product, on account of its prolonged contact with the liquid.
Moreover, these devices are intended for processing large shrimp, and are not practical for treating krill. Besides, the one-by-one manner of processing shrimps curbs the final output, to say nothing of its being labor-consuming and economically ineffective.
There is a further known apparatus for recovering the meat of crustaceans (cf. the DE Patent No. 2,430,095; Int. Cl..sup.2 A 22 c 29/02, published in 1976), comprising a loading mechanism and a mechanism for destroying the shell and separating it from the meat, including a plain-wall pipe with a rectilinear portion and a branch pipe for feeding the working agent or fluid.
The loading mechanism is in the form of a longitudinal belt conveyor of which the working or load-supporting portion is inclined to both sides of the longitudinal axis, toward the side boards. Arranged alongside of the conveyor belt are successively widening horizontal classification slits, with each slit adjoined by an inclined indexing trough.
The mechanism for destroying the shell and separating it from the meat includes a receiving bellmouth adjoined by an oval-section tubular duct of a shape corresponding to the contour of the crustaceans; tangentially introduced into the duct is a branch pipe or nozzle for feeding the working fluid, e.g. compressed air, the rectilinear portion of the duct accommodating the means for destroying and removing the shell, including blade-like teeth and scrapers projecting into the duct, similar to the jaws of a pike. Overlying the nozzle for feeding the working fluid, there are mounted in the duct compressed air deflecting gates, defining a sluice chamber.
The apparatus operates, as follows.
Crustaceans, e.g. crabs loaded onto the horizontal run of the belt conveyor slide down sideways and encounter the successively widening slits which classify them. The first ones to be separated are the smaller species of the crabs, the larger ones being separated subsequently. While sliding down the inclined downward trough, the crabs are indexed and directed into the mechanism for destroying the shell and separating it from the meat. In this mechanism, the crabs indexed to the predetermined attitude are first guided into the receiving bellmouth; then they pass by the compressed air gates and are taken by the compressed air stream which carries them one by one through the rectilinear portion of the tubular duct. While moving through this portion, the crabs engage the blade-like teeth which incise the shell, while the scrapers take it off the body of the crustacean. Then the stripped crabs and the shell fragments are guided to the air blower where lumps of pure meat are recovered by winnowing.
Although the last-described hitherto known apparatus enables one to obtain the meat of crustaceans in the lump form, it cannot be used for processing small crustaceans, e.g. krill.
This known apparatus is intended for recovering the meat of large crustaceans, the necessity of sorting the crustaceans according to their size and the one-by-one fashion of feeding them for processing significantly restricts the output of the apparatus. On account of the tangential arrangement of the compressed air feed nozzle, a part of the air stream is reflected by the walls of the rectilinear portion of the tubular passage and flows in opposition to the advance of crustaceans directed for the processing. This countercurrent impedes the progress of the crustaceans along the curvilinear portion of the tubular duct. For this reason, the known apparatus incorporates gates defining a sluice-like chamber to fight the effect of the aforementioned phenomenon. However, the incorporation of these gates presents an additional resistance to the progress of the crustaceans, which may result in clogging of the receiving bellmouth, to say mothing of its affecting the capacity of the apparatus and complicating its structure.
The cross-sectional shape of the tubular ducts requires precise fractions of crustaceans, which likewise complicates the structure of the apparatus.
Furthermore, the blade-like teeth mounted in the rectilinear portion of the tubular duct are capable of cutting into lumps of the meat of the crustaceans, affecting the integrity of these lumps and stepping up the losses rate, while the scrapers stripping off the shell are susceptible to becoming clogged with shell fragments, which impairs the continuous reliable operation of the apparatus and complicates its sanitary treatment.